Magnetic repeater or compass



F. A. NOXON o MAGNETIC REPEATER OR COMPASS.

Jan.- 1/9, 1943.

Ja'n. 19, 1943. l P, A, NoxoN MAGNETIC REPEATER on coMmss Filed June 15, 1940 4:e sheets-sheet 2 ATTOR Patented J. 19,` 1943 asassc MAGNETIC aannam on coMPAss Paul A. Noxon, Tenaiiy, N. J.,

assigner to Bendix Aviation Corporation, South Bend, Ind., a corporation oi Delaware Application June 13, 1940, Serial No. 340,396

(ci. sei-204) 14Claims.

This invention pertains to magnetic repeaters, particularly a repeating and indicating system for magnetic compasses. l

At the present time, magnetic compasses are generally of two types, the magnetic needle type and the earth inductor type, which utilizes some element other than a magnetic needle, usually a closed coil spinning in the earths iield, which generates voltages that are made to actuate an indicating mechanism to dene a course or to show bearing in azimuth. The magnetic needle type of compass is well imo but has heretofore had many limitations which restrict its usefulness as a navigating instrument. Among the principal disadvantages of the conventional magnetic needle type of compass are the tendency for the card to spin during a turn or upon acceleration of the carrying vehicle, due to the coupling between the compass card and the usual damping liquid in which it rides, which coupling sets up a frictional error known as swirl, and its inability to indicate, or repeat the primary indication of the magnete needle, at a point remote from the compass itself.

These and other disadvantages are overcome by the compass of the present invention as will be described later.

One of the objects of the present invention is the, provision of a follower or repeater of a rotatable magnet which will indicate at a distance and with amplied torque, the position of the magnet with respect to a ixed reference.

Another object is the provision of a magnetic compass of novel design which includes a novel type of pick-up and indicating mechanism which will repeat indications of magnetic heading at a remote station.

Other objects of the invention include the prou vision of means in a magnetic compass system for compensating for deviation and variation errors, and a provision of a novel compass which will give an indication of azimuth through the medium of a torque amplifier.

These and other objects of the present invention will become readily understood upon a study of the following specliication when made in conjunction with the attached drawings, throughout which like parts are designatedby like reference characters.

Fig. 1 is a schematic diagram of the magnetic compass of the present invention; and

Fig. 2 is a schematic diagram of another embodiment 0f the compass of the present invention.

Fig. 3 is a detailed showing of a portion of thel circuit set forth in- Fig. 2, and Fig. 4 is a detailed showing o! thecam compensating mechanism set forth in Fig. 2.

In general terms, there is provided by the present invention, a compass of the magneticV needle type, in which the errorsdue tc swirl, acceleration and the turbulence of the damping liquid are eliminated to all practical purposes. The compass includes one or more magnetic needles carried by any suitable float means in a damping liquid within a closed bowl and has no indicating card attached to the magnets. Closely adjacent l the magnetic needle element there is positioned a magnetic pick-up or iiux gate which, in circuit with a two-phase induction motor, acts to move a .pointer over an azimuth scale at a master station and which, through the incorporation of an Autosyn transmitting and receiving system, provides simultaneous indications of bearing at any desired number of remote stations.

Having particular reference to Fig. l, there is shown at I0 a. compass bowl carrying a magnetic needle II, upon any conventional iioat in any suitable damping liquid. Magnetic needle l! is pivoted by any suitable means, not shown, so that it has an axis of rotation as designated by dotted line I3. A suitable magnet, pivot and iioataris located a pick-up device 444, led May 21, 1940, and signee of the present inventio Flux gate I4 is carried by, and is' capable of rotation with shaft I5 to which is connected a rotor I6 of a transmitting Autosyn Il. The rotor I8 of a two-phase induction motor I9 is connected to a shaft 20 and to shaftl I5, through a speed reducing gear train designated generally as 2|. Flux gate I 4 has an exciting winding, including coils 22 and 23 connectedA in series by means of conductor 24 to through alternator 28, will saturate the portion Immediately below the bottom ofv Apermeable material, such as which maybe of the I. type described in the application Serial Nol.'336,

assigned to the as;

leads 26 and 2l vwhich are, in turn, connected to the output of alter- 5 nator 28. Coils 22 and 23, when energized of pick-member I4 in the region occupied by coils 22 and 23. Member I4 also carries output coils 29 and 36 which are connected in series by means of conductor 3l and to the input of the vacuum tube amplifier 34 by means of leads 32 and 33. A suitable amplifier may be one such as shown and described in Morecrofts Principles of Radio Communication (2nd edition) at page906 or page 942. The output of amplier 34 is connected to one phase 35 of two-phase motor I9, through conductors 36 and 31. The other phase 38 of motor I9 is connected to alternator 28 through a frequency doubler 39. The frequency doubler may be of any conventional type such as that shown and described in pages '106 and '107, Principles of Communication by Morecroft, 2nd edition. Phase 38, during operation of the device shown in Fig. l, is constantly energized through alternator 28, but self-rotation of rotor I8 is possible only when phase Winding 35 is energized by coils 28 and 30, through amplifier-,34. As long as magnet II has its longitudinal axis at right angles to the longitudinal axis of member I4, which condition is represented in perspective in Fig. 1, no resultant voltage will exist in the output of coils 28 and 30, since the magnetic field of magnet II is at right angles to each leg of iiux gate I4, and no flux cuts coils -29 and 30, and therefore no voltages will be generated in coils 29 and 38. When no voltages are generated in these coils, the current ow in phase winding 35 is zero. Thus, phase 35 is deenergized and rotor I8 is maintained stationary. When, however, the craft carrying the compass of the present invention turns in azimuth, there will be a departure of the rectangular relationship above set forth, between magnet I I and ux gate I4, and the magnetic field of magnet II will thread through legs carrying coils 29 and 30 in one direction or the other, depending upon the direction in which the craft is turned. immedi-1 ately there will be a voltage apparent in leads 32 and 33 due to the flux of magnet II flowing through the legs of fiux gate I4 which, after amplification in amplier 34, will energize phase winding 35, causing rotation of iiux gate I4 to its new null position since the direction of the flux, through the legs of flux gate I4, upon disturbance of the rectangular relation, above mencarrying craft is turning, and since the'direction of flux determines the instantaneous polarity of the voltages induced in coils 29 and 30, and thus the polarity of the instantaneous voltage in phase winding 35, it will be apparent that motor I9 can be made to always turn the flux gate I4 in the proper direction to reestablish the rectangular or null relation of the flux gate with the field of magnet Il.

An indicating pointer 40,. movable over an azimuth scale shown partially at 4I, is connected with shaft I of iiux gate I4, so as to be rotatable therewith. Thus, any departure of iiux gate I4 from its null position with respect to magnet II, will cause rotation of the flux gate and consequent indication of this rotation by pointer 48 and azimuth scale 4I. Indicating pointer 48 and scale 4I comprise a master indicator.l Remote indicators, such as Autosyn receivers 42 and 43, can be considered as examples of repeating indicators which may be placed at any desired `stations in an aircraft or on shipboard. Rotors 44 are energized by current from alternator 28 in the-conventional manner, and stators 46 and 41 are connected in parallel to the stator 48 of transmitting Autosyn I1, the rotor I6 of which is also energized by current from alternator 28. As angular rotation of flux gate I4 upon shaft I5 turns rotor member I6 therewith, it will be readily understood that shafts 49 Vand 50, carrying pointers 5I and 52, movable over azimuth scales 53 and 54, will repeat the indications of pointer member 46 and scale 4I.

While the compass system shown in Fig. 1 affords a positive indication of azimuth at any deysirednumber of stations, the embodiment of the invention shown in Fig. 2 has not only the advantages of the system shown in Fig. 1, but it also shows a means whereby corrections iorI deviation errors may be introduced so that the nal magnetic indication need not be referred to a calibration chart, but read directly from the azimuth scale. Also, a means is shown whereby a true magnetic bearing may be converted to a true geographic bearing if the variation between the magnetic and geographic poles is known.

The magnetic compass bowl I8, having needle II, may be of exactly the same construction as the corresponding element shown in Fig. 1. Dlrectly below compass bowl I0, and having its center point located on the axis of rotation I3 of magnet Il, is a pick-up or iiux gate 55, which may be of the type shown in the above mentioned Serial No. 336,444.

The flux gate is shown in detail in Fig. 3 and the lines A and B of Fig. 1 indicate the limits (corresponding to lines A' and B', respectively, Fig. 3) of the detailed showing of Fig. 3. Winding I8 is carried in a three-part section upon the inner portion of each of legs II', I2' and I3' and leads 56 are connected to alternator 28, and the ampere-turns of winding I8' and the current from alternator 28 are so related that periodic saturation of the inner or armature portion I4' of flux gate 55 is eected when, during each halfcycle of alternation the current from alternator 28 reaches the value adequate to cause complete saturation of armature portion I4.

It is understood, of course, that in each halfcycle, current rises from zero to maximum and falls to zero, and any desired value of current may be established as the saturating value. Output windings I5', I6' and I1' are carried by legs II', I2 and I3', respectively, and the inner end of each of these coils is connected to ground while the outer ends of these coils are connected by means of leads 51, 58, and 59 to the circuit of Fig. 2 as designated by the numerals 51, 58, and

59 in Fig. 2. It will be understood that upon.

periodic saturation for a portion of each halfcycle of alternation of alternator 28, armature I4' becomes saturated, resulting in a great change of reluctance of the armature I4', and therefore of the number of lines of flux therein due to the field of magnet II.` Due to this change of reluctance, the flux which prior to saturation, threaded through legs II', I2' and I3', will leave these legs and will thereby induce voltages in coils I5', I6', and I1', which voltages will vary upon rotation in the field of magnet II in accordance with the well known cosine law of variation.

Leads 56 from .he inner or exciting winding are connected to ilternator 28, and leads 51, 58 and 56 from the outer windings (output coils) of flux gate 55 are connected to the stator 60 of Autosyn 6I, as shown schematically in Fig. 2. Coil 62, carried by rotor member 63, is connected through leads 64 to the input of vacuum tube amplifier 34, the output of which is .connected roneous magnetic bearing.

through leads 65 to phase winding 35 of the twophase induction motor I9. The other phase winding 38 is continuously energized by alternator 28 through frequency doubler 39 and leads 66. Induction motor I9 is operatively connected through speed reducing gear train 2| to a shaft 61 which, by any conventional coupling means 68, is connected to another shaft 69. 'I'his shaft 69 is, in turn, coupled through a planetary gear train 10 to shaft 1| carrying pointer 12. Y

As so far described, and in view of the explanations contained in the above identified applications, it will be apparent that the voltages induced in the output coils of flux gate 55 will be connected through leads 51, 58 and k59 with stator 60, and will induce a resultant voltage in coil 62 of rotor 63. The resultant voltage or current is amplified by means of vacuum tube amplifier 36, the output oi which may be of any power rating desired, so that phase winding 35 can be energized to turn rotor i8 of induction motor i9, and also shafts 61, 6d and 1|, causing indicating pointer 12 to indicate bearings in azimuth.

When magnetic needle is situated in an environment that distorts the earths magnetic field, errors due to deviation of the earths eld will, unless corrected, cause pointer 12 to give an er- In order to correct the errors due to deviation, the cam correcting mechanism 13 is introduced so that pointer 12 will be advanced or retarded by the number of degrees necessary to change the apparent magnetic heading to the correct magnetic heading. This correcting mechanism includes cam track 16, which is supported at intervals of 10 or l5 degrees, by clamp members 16 having adjustable screw-threaded Shanks engageable with the annular supporting ring 16. which ring, while shown broken partly away, is circular and is carried by a conventional instrument casing, not shown. A cam follower, such as a roller member 11, is carried by a flexible linkage shown in detail in Fig. 4, wherein a sleeve member 19, integral with an arm |00, tightly embraces shaft 69 so as to turn therewith. Arm |66 is connected to a crank-arm by means of a loose link |02. A spindle |63, extending angularly from crank-arm itl, carries cam follower 11 which is journaled to the end portion thereof. Crank-arm |0| has an integral hub member it which is pivotally secured with respect to the disc portion of scale 86 byvmeans of a pin member |65 extending through hub member |06. Hub member'll has a second crank-arm |66 integral therewith, to which is attached, at its outer end, a coiled spring member 8| with one end anchored to disc portion of scale 86 by means of an upstanding pin member |61. Cam follower 11 is urged against cam track 14 by means of spring member 6| connected between a crank arm'of linkage 18 portion of scale 86. Hub portion of scale 8G has connected thereto a hollow shaft 32' which carries rotor 63 of Autosyn 6l.

Pressure upon cam follower 11, which is exerted radially of shaft 69, will cause crank-arm |0| and crank-arm |66 to be rotated as a unit about pin member |65. Motion is transmitted from cam follower 'i1 to these crankarms through spindle. |63. Assuming that the radial pressure exerted is toward the axis of shaft 69, crank-arm |0| will tend to be rotated clockwise, but since shaft 66 can be rotated only under control of motor IQ while scale 86 is free to'move, scale 80 will be rotated in a counterclockwise direction, and since scale portion 86 and the hub carries the rotor 62 of Autosyn receiver 6| upon the shaft 82, rotor 62 will be moved counterclockwise through the 'same angle that scale'BD moves. If we assume that rotor 63 was at rest prior to the exertion of the radial force upon cam follower 11, it will be appreciated that a voltage will be set-up in coil 62, which, after amplification in amplifier 34, will energize phase winding to cause rotation of shaft 69 through the same angular amount, but in the opposite direction from the direction of scale 80 in Winding 35 being de-energized, rotation of shaft 69 ceases, but this rotation (due to radial pressure upon cam follower 11) has caused pointer 12 to move by the angular amount necessary to offand if cam follower 11 has been moved radially by an amount sufficient to make pointer 12 now indicate the bearing corrected for deviation (which deviation, of course, is known), then scale 66,' after rotation of shaft 66 has stopped, will have again turned clockwise so. that under its index, scale 80 reads the same as it did prior to its counter-clockwise motion. We see then that in this particular case, motion of scale 80, counter-clockwise and carrying rotor 63, has caused induction motor |9-to operate to restore rotor coil 62 to its null position, and has therefore turned shaft 69 clockwise, land in so turning it returns scale 86 in a clockwise direction through the medium of the linkage above described. It is because of this follow-up action of scale 80 that the bearing read thereon is the uncorrected,

l rather than the corrected,bearing which is read Because of spring member 8|, motion of cam follower 11 in a from pointer 12.

which yields upon direction radially low shaft 69 through the linkage including members |00, |0| and |02, without lost motion. The tension of spring 6| may be so adjusted that l scale 80, which carries only the small load irnposed by the bearings of shaft 82 and rotor 63.

may readily be rotated upon rotation of shaft 69.

In order to correct the magnetic bearings so that the correct bearingsl may be read from pointer 12, the adjustable screw threaded Shanks of clamp members 15 are adjusted radially of shaft.; 69 within lthe instrument casing (not shown) so that cam track 14 may be made to follow the proper contour to effect corrections at every 10 or 15 degree points, in accordance with the well known practice of deviation correction which is common in the art. It is believed that one skilled in the art will appreciate the steps of swinging ship and adjustment of members 15, necessary to cause cam follower 11 to impart through the rotation ofscale 86, its shaft 82', and rotor'member 63, the necessary motions to compensate for the deviation errors peculiar to each compass installation.

As an example of the process of correction, let us assume that the bearing reading on scale 89 is lzero degrees, and that pointer 12 has not been corrected for deviation and therefore indicates a bearing of zero degrees. If, from an appropriate deviation chart or curve, it appears that at an indicated bearing of zero, the corrected bearing is 350 degrees, adjustment is made to the threaded shank of clamp 15 corresponding to the zero degree position. by screwing it in radially order to restore coil 62 to its null position, at which point, phase of shaft 69, scale will foluntiltscale 80 moves counter-clockwise to the 350 degree position. This carries shaft 82 and rotor 62 ten degrees counter-clockwise from the null positionl and upon energization of the system (assuming no change in course) induction motor I9 rotates rotor 62, by movement of Shaft B9 and scale 8U, clockwise ten degrees, restoring rotor 62 to its null position and scale 98 to its zero degree position. Since, before this clockwise motion, pointer 12 was on zero course, it will have been moved ten degrees counter-clockwise, or to the 350 degree, or corrected, position. Pointer 12 moves counter-clockwise upon clockwise rotation of shaft 69 as the planet train 10 causes reversal of rotation of shaft 1 I, as can be readily seen from an inspection of Fig. 2. Cam member 14 may be of spring steel and its surface will readily conform to adjustment, resulting in a smooth track for roller 11. Thus, scale 88, at any time, will indicate the apparent magnetic. bearing uncorrected for magnetic deviation, while rection into the repeating system, including remte Autosyn indicators 42 and 43. At the same time, the correction for variation can be observed through a window 95 in the face of scale 89. The amount of variation correction introduced may be gauged by any suitable index, not shown, on the face of scale 83.

It will be seen that by the magnetic compass system shown in Fig. 2, both master and repeater indications of magnetic bearing, corrected for deviation errors, may be had, and if the variation between the magnetic and geographic poles is known, then the pilot or operator may introduce this correction at the master station and all readings thereafter, whether at the master, or at any of the repeater stations, will be referred to the earth's geographic, rather than the earth's pointer 12 will move over scale 83 by the' angle necessary to indicate the bearing corrected for magnetic deviation.

Scale 83, which may be called the master indicator scale, therefore reads correct magnetic bearings and by the use of an Autosyn transmitter II having its rotor I6 connected so as to be rotated upon shaft 61, a repeating system, including Autosyn receivers 42 and 43, as described in connection with Fig. 1, may be provided. It is felt that further explanation of this repeating system is unnecessary at this point.

A manual adjusting knob 84 is provided with a shaft having a pinion 85 engageable with a gear 86 and teeth on course selecting disk 81, having grid or lubber lines 88, and a course pointer 89. By this adjusting mechanism, any desired course can be selected and will be indicated by the position of pointer 89 upon azimuth scale 83. If it is desired to steer the course indicated by pointer 89, then it is necessary only to keep pointer 12 parallel to grid lines 88.

Correction for variation is obtained through the medium of the following mechanism:

A supplemental scale 90, which contains graduations designated as degrees, which may be indicative of degrees east and west variation, has teeth on its peripheral edge engaging with a pinion 9| to which is connected a shaft 92, having a pinion 93 at its end remote from pinion 9|. Pinion 93 is engageable with teeth formed upon end-plate 94, which end-plate is rigidly xed to the stator casing of Autosyn I1. Pinion 85 may be advanced into engagement with pinion 9|, as indicated by the dotted lines, upon depression of manual adjusting knob 84. When knob 84 is so depressed, and is rotated by the amount of rotation corresponding to the correct number ofy degrees of east or west variation applicable, the stator casing of vanced or retarded by the same number of degrees. By means of the planetary gearing 10 rotation of scale 90 by means of adjusting knob 84 does not aect the setting of pointer 12 when dial 90 is at rest. Motion is transmitted through the spur gear carried on the end of shaft 69 through the intermeshing pinions which are included in the planet gearing and to the spur gear carried upon shaft 1I. When scale 9|) is in angular motion, the intermeshing planet gear arrangement 10 rotates freely about the gears of shafts 69 and 1I without causing either shaft 89 or 1I to be rotated. Rotation of the stator of Autosyn I1 introduces the proper variation cormagnetic pole. By this system, a particular compass installation eliminates the 4necessity of a calibration chart. as corrected readings may be taken directly from scale 83. At the same time, the uncorrected readings may be read from scale 80, so that at the time of installation, the amount of correction for deviation at any point in azimuth 4prime mover.

may be observed.

In describing the embodiments of the compass shown in Figs. 1 and 2, it has been assumed that axis I3 passes vertically through the center of ux gates I4 and 55, and through the center of rotation of magnetic needle II. This condition is true, of course, when the carrying aircraft or ship is in a. steady, level condition. Of course, during intervals when the carrying vehicle pitches and rolls, axis I3 departs from the true vertical, but this means merely that magnet |I and flux gate I4 or 55 are no longer in parallel, horizontal planes. However, as long as the flux gate is in the closed magnetic eld of magnet II, true operation of the compass results regardless of whether or not the ux gate is maintained horizontal with respect to magnet II. It is believed that this is apparent to those skilled in the art of navigation without further explanation.

The above description has been limited to a magnetic compass. However, the present invention is equally well suited for use in any system requiring a primary or remote indication of the position of a magnetic needle with or without torque amplification, without reaction upon the For example, if it is desired to repeat the indication of a sensitive galvanometer, this result may be accomplished by the substitution of a magnetic needle for the usual galvanometer needle, and the pick-up device, or flux gate I4 or 55, when placed within the influence of the magnetic field of the needle, will repeat the indications it will repeat the indications of the system when used as a compass.

While only two embodiments of the present invention have been shown, it is to be understood that the invention is not limited to these examples, but by the scope of the appended claims.

What is claimed is:

1. A magnetic compass comprising a magnet disposed in the earth's magnetic eld, a pick-up device of permeable material mounted within the field of said magnet and threaded thereby, a

source of alternating current. means in circuit therewith and included in said pick-up device for periodically saturating and unsaturating a portion of said permeable material, whereby the eld of said magnet is alternately expelled from and threaded through said pick-up device, coil means on said-device separated from said saturating thereof in the same manner that 'magnet a transmitting means and inductively related to said pick-up device, and 'an indicating device having coil means conductively connected to the rst-mentioned coil means, a coil inductively coupled to the second-mentioned coil means for designating the direction. of the field of said magnet and an index connected to said inductively coupled coil.

2. A magnetic compass comprising a magnet disposed in the earth's magnetic ield, a pick-up device within the inuence of the field ofsaid Autosyn, an induction motor, shafts having a common axis about which saidpick-up device, transmitting Autosyn and induction motor are rotatable as a unit, said pick-up device being of permeable material and having means associated therewith to alternately saturate and unsaturate a central portion of said device and coil means in which are induced voltages depending on the angle of rotation between said magnet and an axis oi' said pick-up device, an ampliiier having its input connected said coil means and its output to said induction motor, whereby said shafts may be rotated, a

pointer rotatable with said shafts to indicate direction in azimuth, a transmitting Autosyn having its rotor connected to rotate with said shafts, an Autosyn receiver having a stator and a rotor, the stators of said transmitting and receiving Autosyns being electrically connected together, and an indicating member carried by the rotor of said receiving Autosyn, whereby upon movement of said shafts, said indicating member will indicate the angular movement thereof,

3. A magnetic compass including a magnet disposed within the pick-up device of permeable material located in proximity thereto so as to be. inuenced by the Vfield of said magnet, means for periodically saturating a portion of said pick-up device, coils on said device, an Autosyn receiver having a rotor and a stator, said coils being electrically connected to said stator, a winding carried. by said rotor, a vacuum tube amplifier, an induction motor having two-phase windings, means for exciting one of said two-phase windings with alternating current, said winding carried by said rotor being connected to the other of said twophase windings through said vacuum tube amplier, a transmitting Autosyn having a stator section and a rotor section, shafting common to said induction motor and said rotor section, a second receiving Autosyn having connections to said transmitting Autosyn and an indicator, cam means for compensating for magnetic deviation and a second indicator associated therewith for giving a reading of magnetic heading corrected for deviation, and selector means operable to introduce correction of said magnetic heading to headings measured with respect to geographic meridians, and means activated by said selector means to rotate said stator section of said transmitting Autosyn, whereby the indicator associated with said second `receiving Autosyn will read headings with respect to geographic meridians.

4. A magnetic compass comprising a magnet, a pick-up device of permeable material adjacent said magnet, and within the iniiuence of its magnetic iield, a motor in circuit therewith and having two phase windings and a rotor associated therewith, means for energizing one of said phase windings with a constant alternating current, coils carried by said pick-up device and energized by alternating current to alternately saturate and unsaturate a portion of said pick-up earths magnetic iield, a o

device, windings carried by said pick-up device in which are induced voltages due to the varying of the iield of said magnet in response to the saturating and unsaturating of said portion, elec.- trical connections between said windings and the other ofrsaid two-phase windings, a shaft means securing said pick-up device to said shaft, and indicating means associated with said shaft, whereupon as said rotor is rotated, said indicating means will show the angular displacement of said shaft. v

5. A magnetic compass including a magnet, a flux gate of permeable material disposed in closeproximity thereto, said magnet and said ux gate having a common axis of rotation, said` V magnet being rotatable in azimuth with respect to said iiux gate in response to the directive iniiuence of the earths magnetic eld, a motor having a rotor and stator, means associated with said flux gate and the stator of said motor to l operatesaid rotor when said magnet and said ux gate have been relatively displaced from a null position,. and indicating means controlled by rotation of said rotor to designate angles in azimuth.

6. A magnetic compass comprising a magnet mounted for free response in azimuth to the directive force of the earths magnetic iield, a ux gate disposed within the field of said magnet, an indicator of azimuth, and motor means controlled by said flux gate to move said indicator in azimuth in response to relative rotation betweensaid magnet and said flux gate.

7. A magnetic compass comprising a magnet freely rotatable in azimuth, a flux gate .within the iniiuence of the eld of said magnet ineluding a member of permeable material, exciting and output coils thereon, a motor, an indicator of azimuth, connections between said output coilsandsaid motor, and means connected to said exciting coil for intermittently saturating a portion of said flux gate, whereby an alternating current is induced in said output coils, and operates said motor to control the rotation of said indicator of azimuth.

8. A magnetic compass comprising amagnet having an axis of rotation and being mounted for free rotation about said axis in response to the directive force of the earths iield, a iiux gate oi' permeable material having 'the same axis of rotation, said flux gate being within thefield of said magnet, a motor, a shaft connecting said 'motor and said iiux gate, an indicator controlled by movement of said motor, and means responsive to relative rotation between said magnet and said flux gate to rotate said iiux gate and actuate said indicator of azimuth.

9. An indicator of the direction of a magnetic` iield includingv a magnet having a directional magnetic iield and being mounted for free rotation about avxed axis, a iiux gate of permeable material disposed withinv the influence of said magnetic field and being symmetrical about said axis, an exciting winding and output windings on said flux gate, a motor, an indicator controlled thereby, connections between said output coils and said motor, and means in circuit with said exciting winding for intermittently saturating a portion of said iiux gate, whereby voltages are induced in said output coils and control said motor and indicator to show the direction .of the field of said magnet.

10. An indicator ofthe direction of a magnetic eld comprising a magnet, a pick-up device of permeable material located within the in- 6 asoaeoc iluence of the field of said magnet, an exciting disposed in magnetic relation with said compass winding and output coils carried by said device, magnet, whereby the latter induces a magnetic an indicating element and a motor having a rotor iiux therein, coil means on said core means havfor controlling movement of -said indicating eleing an input and output, a source of periodically ment, and a stator member having polyphase varying current connected to the input of saidA windings, a source of alternating current concoil means for periodically varying the magnetic nected to one of said polyphase windings, said flux in said core means, whereby an alternating source of alternating current having a branch current is generated at the output of said coil connected to said exciting winding, wherebysaid means as a function of the relative rotation bewinding intermittently saturates a portion of 10 tween said compass magnet and said core means, said pick-up device, and said output coils being an electromagnetic device having a rotor and a connected in a circuit including'another of said stator and being connected for energization by' polyphase windings to control the rotation of said periodically varying current and by said gensaid motor, erated alternating current, whereby the rotor 11. A magnetic compass including a magnet thereof is actuated upon relative rotation bedisposed in the earth's magnetic ileld and mounttween said compass magnet and said core means,

ed for free rotation in response to the directive and means drivably connected to said rotor for force of the'earths iield, a permeable pick-up actuation thereby.

member within the influence of the field of said 14. A magnetic compass repeater system commagnet, means carried by said pick-up member prising a compass having a magnet rotatable unfor intermittently saturating a portion thereof, der the iniiuence of the earths magnetic iield, coil members carried by said pick-up member, a core means of magneticallvpermeable material motor, an indicator driven by said motor, and disposed in magnetic relation coaxially with said connections between said motor and said coil compass magnet, hereby the latter induces a members, whereby rotation of said motor is unmagnetic flux therein. coil means on said core der control of said pick-up member. means having an input and output, a source of 12. An indicator of magnetic direction comperiodically varying current connected to the inprising a magnet freely mounted to be responput of said coil means for periodically varying sive to an external directive force, a ux gate of the magnetic flux in said core means, whereby permeable material disposed within the influence an alternating current is generated at the outof the field of said magnet, said magnet and flux put of said coil means as a function of the relagate having a common axis of rotation, a motor tive rotation between said compass magnet and having a rotor and a stator, means associated said core means, an electromagnetic device comwith said flux gate and the stator of said motor DrSing a rotor and a stator having a multi-Part to operate said rotor when said magnet and said 3:, winding. one of said parts being connected for ux gate have been relatively displaced from a energization by said perlodicallyvarying current null position, and indicating means for showing and the other of said parts being connected for the relative angular displacement between said energizationby said generated alternating curmagnet and an arbitrary index. i rent, whereby said rotor is actuated upon rela- 13. A magnetic compass repeater system com- 40 tive rotation between said compass magnet and prising a compass having amagnet rotatable unsaid core means, and means drvably Connected der the influence of the earth's magnetic field, to said rotor for actuation thereby. core means of magnetically permeable material PAUL A. NOXON. 

